Investigating the effect of concentration of acid on the Rate of reaction

Free essay example:

Investigating the effect of concentration of acid on the

Rate of reaction

Plan

Method

For my experiment, I will be investigating rate of reaction, I will do this using HCl (hydrochloric Acid) and limestone chips (CaCO3) there are many variables that can affect the rate of reaction, they are – Surface area of marble chips, strength of acid, temperature. The quicker that the CO2 (Carbon Dioxide) is produced, the quicker the rate of reaction between them is. For my investigation I will investigate how the strength of acid affects this reaction, I will use 5 strengths of acid, 0.25 Molar, 0.5 Molar, 1.0 Molar, 1.5. Molar and 2.0 molar, for a control I will use 0 Molar acid, or water, I would expect the rate of reaction to be zero for this, and it will only be used to prove that it is the acid that is reacting with the chips, not another variable. I will pour the acid into a conical flask with the marble chips. I will then collect the CO2 released in a measuring cylinder as shown in the diagram below. Alternatively, I could use a gas syringe, but these are expensive, and fragile. So instead I will use a plastic measuring cylinder. I will take readings at intervals of 10 seconds for a set period of time or until the reaction has stopped.

Diagram

Prediction

My Hypothesis is that the higher the concentration of acid, the faster the rate of reaction. This is because the higher the concentration of acid, the more particles of HCl will be colliding with the marble chip which means that there are more reactions taking place, so more CO2will be produced. I will also predict that the rate of reaction should double if concentration is doubled; this means that for instance it takes 1.0 Molar Acid 50 seconds to create 100cm³ it should then take 2.0 molar acid 25 seconds to create the same volume of gas. My hypothesis is supported by the collision theory. The collision theory is a principle concerned with rates of reaction. During reactions, there is a solution of the reactant and the reactor, in the case of this experiment, the marble chips and the hydrochloric acid respectively. During the reaction, particles from each hit each other and release energy. This is the reaction; it will release the energy as heat. The formula for the reaction is CaCO3+ 2HCl=CaCl2+ H2O+ CO2. So the reaction will give of water and carbon dioxide, the carbon dioxide is the reason that there are bubbles appearing around the marble chips. As the gas is produced, since the conical flask is full of air, the carbon dioxide produced will force gas out of the conical flask, through the delivery tube, and into the up turned measuring cylinder, as the cylinder is full of water, it will “push” the water out. By reading the volume of gas produced, you can see how fast the marble chips and HCl are reacting.

In the diagram above, the HCl particles are represented by the red circle, and the blue circle represents the particles of marble chips. The particles are moving around and as they hit each other, there is a reaction.

Certain variables will affect the reaction, such as temperature, this will give the particles more energy so they will move around faster, allowing more reactions. The surface area of the chips will affect the reaction.

As if there are twice as many reactants in an area, there should be double the amount of reaction, as there are twice as many acid particles in the same volume of acid.

Background

As the surface area has doubled, the amount of area that the reactions is taking place on has increased, this will increase the rate of reaction.

Strength of acid can affect the reaction.

By doubling the strength, the number of HCl particles are increased, this means that there are more particles to react, increasing the rate of reaction.

Background

From previous science experiments, I know that to make this a fair test, the other variables (Surface area of marble chips, strength of acid, temperature), will need to be controlled, if they are not, then they will affect the results; increases in surface area allows a reaction across a larger area, thus increasing the reaction rate, increases in strength of acid will increase the number acid particles that will react, an increase in temperature will increase the energy that the particles have, this means they will move faster, and there will be more collisions. If these are not controlled the results will not accurately reflect the affect that concentration has on rate of reaction.

For my experiment I will need:

Conical flask

A bung

A delivery tube

Container of water

Measuring cylinder

Stopwatch

I will use 5 concentrations of acid and a control as I stated earlier, taking readings of the amount of CO2 collected every 10 seconds. I plan to repeat the experiment at least twice to prevent anomalous data on the results.

Analysis

The aim of my investigation was to investigate the reaction of CaCO3, from my results; I can see that my experiment went well. As a basic pattern, the rate of reaction is proportional to the concentration of acid. Across all my results, there is the trend that higher concentration produces higher rates of reaction. In my prediction I stated that in theory if concentration doubles, the rate of reaction will double I will check this in my results, by sampling data randomly from the averages table. I will then compare the results, if the increase is 2x, then the data follows the theoretical increase.

160s2 Molar- 285.67

1 Molar- 85.00

To prove my prediction correct, the result for 2 molar should be 170cc, for the hypothesised increase of 2x, when it is actually closer to 3x.

230s0.5 Molar – 28.67

0.25 Molar - 8.33

Again the increase is around 3x, instead of 2x.

280s 0.5 Molar 31.33cc

0.25 Molar 10cc

Again the increase is ~3x.

250s 2 Molar 320cc

1.5Molar 160.33cc, the results here is doubled, but the increase of the concentration is not double.

From the sampled data above, it is clear that my results supported my qualitative prediction; none of them supported my quantitative prediction.

On the graphs it is shown that the graphs are the shape that would be expected but unfortunately the results vary a lot between each repeat that I did. One of the examples of this is the repeats for 0.5 molar, with the last repeat lasting almost 3minutes longer than the 2nd repeat. And for the 0.25molar results, the first repeat produced no CO2, but the other repeats, it did.

I have worked out the tangents for the averages graph and can use these to compare each trend line.

Acid Strength

2 Molar

1.5 Molar

1 Molar

0.5 Molar

0.25 Molar

Tangent

2.44

0.8

0.56

0.16

0.02

From the tangents, and the data sampled from my results. I can say that my results did not follow the trend that I would have expected if the experiment went perfectly.